(1) Field of the Invention
The invention relates to a method and an apparatus for radiation curing.
(2) Description of Related Art
WO 02/32641 A1 and the publication by Erich Beck et. al., “UV-curing in Carbon dioxide” disclose a method of radiation curing in which containers open on one side are used, with the opening at the top or bottom depending on the inert gas involved. The parts to be irradiated are inserted in these containers. In this process, the parts provided with a coating to be cured pass through an entry zone, a radiation chamber and an exit zone. The radiation chamber is provided with one or more irradiation sources for radiation curing, and a gas inlet for the entry of inert gas.
In WO 02/32641, the aim is to avoid the entry of oxygen into the radiation chamber, since reactions with oxygen during curing are undesired and lead to poor results. For this purpose the radiation chamber is designed as a tower, with a bottom section connected to the entry zone and the exit zone, and the irradiation source located in its top section. The parts are therefore fed in to the irradiation chamber from the bottom to the top, while the radiation chamber is open only at the bottom. This should prevent convective or turbulent gas flows which, in the prior art, are supposed to lead to the escape of inert gas and the inflow of oxygen. The inert gas is meant to be fed continuously into the top section of the radiation chamber, where it forms a displacement cushion against oxygen areas of the gas. It is also possible to provide gas curtains.
Known from DE 10 153 878 B4 is an installation for radiation curing with a radiation chamber and which has an irradiation zone with one or more irradiation sources for radiation curing, together with an entry zone and an exit zone on either side of the former, for the guiding in and out of parts provided with a coating to be cured. The entry zone and/or the exit zone are in the form of inert gas locks, with an outer jacket tube and an inner jacket tube at a distance from the outer jacket tube so as to form an annular gap. On that side of it facing away from the irradiation zone, the inner jacket tube is connected to the outer jacket tube so as to be substantially flow-tight, while the annular gap is connected to one or more gas input lines for inert gas. A radiation chamber according to this prior art has a device for feeding the inert gas into the radiation chamber, while the base area of the radiation chamber has a gas outlet line to take away gas which has become impure or mixed with incoming oxygen. To further reduce the oxygen concentration in the radiation chamber, an inert gas lock is provided in both the entry zone and the exit zone.
DE 34 27 315 A1 discloses in order to improve a continuous system for treating coated mouldings with high-energy radiation under an inert gas atmosphere, having a conveying zone, an irradiation device arranged in the course of the conveying zone and having a channel system which encloses the conveying zone in the region of the irradiation device and has an inlet channel extending from an inlet opening to the irradiation device and an outlet channel extending from the irradiation device to an outlet opening and into which channel system inert gas can be introduced in the vicinity of the irradiation device, in such a manner that a higher throughput of mouldings per unit time can be achieved. It is proposed to provide the inlet channel and the outlet channel with, in each case, an injection opening for inert gas and to provide, in each case, an extraction device in the vicinity of the inlet opening and of the outlet opening so that the inert gas introduced into the inlet channel and the outlet channel flows substantially towards the corresponding inlet opening and outlet opening respectively.
The disadvantage with the methods according to the prior art is that the locks provided, also the inflow and outflow systems, are unable to prevent the entry and subsequent inflow of atmospheric oxygen and a creeping contamination of the atmosphere. In addition, a large volume of inert gas must be supplied on a continuing basis, but is then able to escape for example at the gas locks. The methods are therefore relatively inefficient.